It is a marshall JCM 2000 DSL 401 all tube amp. I went to bed and left it on, the next night I went to use it I found it on and not working. The power amp tubes light up but the pre amp tubes do not. I havent replaced the tubes do you think they are the problem. Thanks, dhu1988
There is a bridge rectifier and red and black wires jumping from preamp tube to preamp tube. These need to be resoldered, take it to your favorite pro audio service center. I'm doing this to the same amp right this minute!
Send it to me, I'll fix it.
770 451 5057
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Likely the filter capacitors have a problem. Best to take this in for repair... it is ODD that there is noise with the standby switch is in standby... That makes no sense... In standby it appears that power is removed from the power amp high voltage so nothing should come through the speaker... Unles maybe one off the power tubes had a total meltdown which should have blown the fuse.
I doubt that you have checked the tubes... tube checker's are rarity now and you can't look at a tube and "tell it is alright". If you leave the footswitch out does it do the same thing?
The probllem could be many things...and you haven't mentioned how you tested the items you are exhonorating. A common problem is a noisy or broken INPUT jack. Musicians forget to loop the guitar cord through the handle and the cord gets moved and yanked sideways wearing the jack and often breaking internal parts. Yjos also goes for the cord to the footswitch as well. Cords and connectors/jacks are the common problems. Less common but frequent are damaged volume control pots due to damage when handling... including broken solder where these attach to the circuit boards.
Since you are getting some output, the amp section is probably OK. There are circuits designed to handle thge difference impedence outputs. This should be a relatively simple repair for any shop that handles these units. If you don't have one local to you, let me know and I'll locate the service info and get you more specifics.
Most 1960 cabs have an option for 8 or 16 ohm... i dont think there is a 4 ohm option. The Jcm 2000 heads have the ability to do all three ohm setting. Thats all you really have to worry about. Make sure the ohms match up. The 1960 cabs typically have 4 t-75 speakers in them which are 75 watts each so wattage is not a problem. There is some argument about what ohms sound best. It doesn't really change that much in the sound in my personal opinion. I run mine at 16 ohms though cause i think it sounds brighter...
try to find any diagram from a website.. then print it and give it to your amp tech. so he could Identify what are the wrong, what the first guy did to your amp and its better to buy a whole new tubes. I know your amp tech is very good. I'm just a noob about tubes yet I want to know how this works. hoping for the best for your amp tube.